Electron discharge device



April 19, 1949. w, SHQUPP 2,467,538

ELECTRON DI SCHARGE DEVICE Filed May 10, 1947 ATTORNEY BYW I Patented Apr. 19, 1949 ELECTRON DISCHARGE DEVICE William E. Shoupp, Wilkinsburg, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 10, 1947, Serial No. 747,255

'7 Claims.

This invention relates to electron discharge devices generally referred to as magnetrons, and more particularly to tuning means for the same.

Even though improved manufacturing processes have attained more accurate fabrication of magnetrons, the tolerances necessarily allowed, or other causes, introduce frequency differences in magnetrons, which are even more aggravated in connection with production of oscillations of extremely short wave length, especially where the wave length is measured by not more than one digit in centimeters. Tuning of the magnetron to an intended precise or narrow band frequency after the magnetron is entirely assembled, on test or in use, is highly desirable. It is likewise desirable to be able to tune a magnetron while in use, from one precise frequency to another. Attempts have been made heretofore to obtain tuning by mechanical means within the magnetron operated by external control.

The present invention relates to and has for its object the tuning of a magnetron by electronic means, and more definitely tuning by injecting electrons into capacitative elementsof a magnetron thereby altering resonant frequency of the oscillating element or elements. It is common practice in magnetrons to provide ringshaped straps in an end space thereof and in the present disclosure ring-shaped coaxial straps are provided of which one strap connects alternate partitions provided between cavity resonators and of which another concentric strap connects the intervening partitions. These straps have a mutual capacitance as well as a capacity relationship to those of the anode partitions which are alternately skipped by each ring. According to my invention tuning is accomplished by placing a special or auxiliary cathode in the end space next the straps directed toward the associated portions of the anode partitions of the magnetron and applying a modulation voltage between said auxiliary cathode and the magnetron anode. The electrons from the auxiliary cathode will be drawn toward the anode and will enter the spaces between the straps and also form a conductive path from the straps to the anode at the separated regions of straps and anode. If the frequency is somewhat less than the Lamor frequency, the electrons will have small radial amplitude due to the very strong magnetic field applied for magnetron operation and will travel in tight helices the general directions of which are roughly straight paths. I propose using the presence of these electrons between the capacitative elements of the inherent resonant circuits to cause the desired change in resonant frequency of the magnetron due to alterations of the dielectric constant and thereby obtain a frequency shift or tuning.

In addition to the broad object of obtaining electronic tuning by capacity variation at the straps, the invention contemplates obtaining frequency shift in proportion to electron current along a short path and readily controlled modulation power supply therefor.

Other objects of the invention will appear to those skilled in the art to which it appertains, as the description proceeds, both by direct recitation thereof and by implication from the context.

Referring to the accompanying drawing in which like numerals of reference indicate similar parts throughout the several views;

Figure 1 is an axially longitudinal section of a magnetron showing my improved tuning means therein;

Figure 2 is a plan of the construction of Figure l, but with the cover or end plate removed, as on line IIII of Figure 1;

Figure 3 is another cross-section as on line III-III of Figure l Figure 4 is a further cross-section as on line IVIV of Figure 1;

Figures 5 and 6 are enlarged detail sections of a portion of the auxiliary or tuning cathode at non-emitting and electron emitting areas respectively and showing an associated portion of the anode, as on lines V-V and VI-V I respectively of Figure 3; and

Figure 7 is a further sectional view similar to Figure 6 at another emitting portion of the oathode taken on line VIIVII of Figure 3.

In the specific embodiment of the invention illustrated in the several figures of the drawing, the reference numeral l0 designates a cylindrical metallic magnetron body, the ends whereof have cover or end plates ll sealed thereon that the interior may be evacuated. Within and as an integral part of said body is the usual magnetron anode structure I2 of generally cylindrical shape but shorter than the outer part of the body so as to provide end spaces [3 between the anode and said end plates II. The anode structure is axially hollow to provide a cathode cavity I4 and radiating from the cathode cavity are a plurality of cavities l5 constituting cavity resonators each having, in the form shown, a cylindrical portion having a longitudinal constricted capacitative slot l6 constituting a lateral opening from the cylindrical portion of the cavity into the hollow central part of cathode chamber-of the mag- In consequence of the several cavities provided in the anode, the structure provides a plurality of partitions or vanes I"! radiating from the central or cathode cavity l4 intervening between and at least in part forming walls for the several cavities. t the ends of the vanes l1 and adjacent the interaction chamber or end space l3 are provided, at each end of the anode, double ring straps, identified as outer or larger strap I8 and,

a coaxial inner or smaller strap l9. The primary purpose of these straps is to achieve large mode scp gration between the desired or 1r mode and the lower order modes, and destruction of these lower orders. According to the present invention advantage is taken of the fact that the capacitance between these straps and between the straps and parts of the anode partitions is of consequence in mode determination. It should be noted in this connection, that the vanes are notched or stepped for reception or passage of the straps, and that the straps each alternate in engagement with the vanes and that vanes engaged by one strap of the pair-at one end of the anode are skipped by theother strap of the pair. A capacitance accordingly exists between the skipping strap :and the vane skipped in each instance.

An indirectly heatedcathode 28 passes axially through the cathode cavity l4, adequately spaced from the anode-and supported as usual from leadin rods 2| entering the end spaces or reaction chambers l3 at the sides thereof. An output loop 22 is situated in one of the resonant cavities l5, passing out through the side wall of the body In in accordance with usual practice. The size and shape of the magnetron body, the end spaces, anode, cathode and leads above described are preferably all substantially in accordance with prior art practice, in consequence of which the pole pieces of the magnet, not shown, will have the same or closely the same relation to the magnetron and its anode as exists in magnetrons as heretofore used.

In carrying out the present invention .an auxiliary cathode 23, of generally ring or doughnut shape, is shown concentrically situated in said end space l3, and in this instance, since straps areprovided at both ends of the anode, an auxiliary cathode 23 is located in each of said spaces. The said auxiliary cathode occupies a position circularly opposing the cylindrical end edges of the straps l8, l9 and slotted portions of the anode and preferably'has a radial width substantially equal to the radiallength of said slots. Thus, the auxiliary cathode overlies or opposes those portions of the anode partitions or vanes inter" vening between the straps and also extra margins radially outside of the outer strap and radially inside the inner strap. These extra margins of overlap of the'auxiliary cathode to the straps are atleast as great as clearance distance radially .uitoward t eanode. end andaflan ed t oidal i the torus.

wall 25 on the side of the fiat wall away from the anode. The flanges 26 of the flanged toroidal wall are secured to the flat marginal surfaces of the said flat wall. The toroidal wall is split radially at one part thereof so as to provide separated ends 21 therefor which face toward each other. Coaxially within said toroidal wall 25 and spaced from the flat wall 24 is a heater 28, here shown as a single-strand resistance wire, the ends of which protrude from the two said ends 21 of One of said ends of the heater 28 is connected to the auxiliary cathode casing andthe other end of said heater is connected to a lead-in rod or wire '29 the inner end of which is shown protruding radially of the magnetron end space 3 to a location between ends of the auxiliary cathode casing and out of contact therefrom.

' The interior of the torus or auxiliary cathode casing contains a suitable electrical insulation material 30 for maintaining desired electrical isolation of the heater, except where attachedat its one end, from said casing of the auxiliary cathode.

Support for and electrical connection to the auxiliary cathode casing is obtained by another radially disposed lead-in rod or wire 3 I. For that purpose a partial sleeve 32 is shown integral with and projecting radially from said torus and this Sleeve is in turn soldered or otherwise secured on the end portion of the lead-in rod or wire 3|. This lead-in rod 3| constitutes electrical connection both for the auxiliary cathode and ,for one end of the heater. The other or first-mentioned. lead-in rod 29 connects only with the other end of the heater so as to obtain a complete heater circuit to the exterior. Insulative mounting and passage of both lead-in wires at each end of the magnetron is alike and accords with prior art practice for lead-in wires as to construction, so requires no elaboration herein.

On the face of the flat wall 24 of the auxiliary cathode directed toward the anode, at the areas directly opposing the ends of the partitions or vanes ll of the anode in the region of an opening toward said straps l8, l9, are cups 33 in the bottoms or upon the basal end walls of which is pro- .vided material 34 copiously emissive of electrons. The cups are welded or otherwise secured at their basal or end walls against the fiat wall 24 and thus confine emissive areas of the auxiliary cathodes to the isolated patches of the emissive material. It is of course understood that any suitable emissive materials may be employed, of which alkaline earths, such as barium or stron-. tium or their oxides are examples.

The side Walls of cups 33 form a continuous rim for each, projecting from the basal end wall around the patch of emissive material and constitute a focusing collar for the electrons. Inasmuch as clearance for skipping of engagement of the rings by the vanes is first on one side of one ring and then upon the other or remote side of the other ring, the successive cups 33 are correspondingly staggered so each will oppose the rings and clearance space for the successive vanes of the circular series.

By virtue of the focusing of the magneticfield and the fact that the restricted emissive areas or patches are directly over the straps and partitions or vanes of the anode with individual focusing collars, emission is beamed into the space between the straps and clearance space next thereto with negligible spreading of the beam or scattering of the electrons. ,Thcelcctronswill be collected at the end of the partition or vane in the stepped part thereof below the strap level. The parallel walls of the straps, and walls of the straps across the clearance to the anode partition constitute the capacitative elements and that capacitance has a determining influence on the electro-magnetic coupling between the cavity resonators. Presence in and passage between said straps and between the straps and anode of electrons, alters the capacitance thereof and thus the coupling is directly affected and the frequency shift will be proportional to the electron current, and can be controlled externally by the modulation power supply to the auxiliary cathode. Attention is called to the fact that while electrons are emitted from the main cathode 2B in a direction radially of the anode body, the electrons from the auxiliary cathode 23 are emitted in an axial direction of the anode body.

Frequency modulation is, therefore, in consequence of the structure described above, produced electronically by means of a separate modulation power supply used in conjunction with the auxiliary cathode, and without need for any moving mechanical parts in the magnetron.

I claim:

3.. A magnetron having an anode providing a cathode cavity and radiating vanes providing cavity resonators therebetween, straps extending between said vanes and constituting capacitative elements, a main cathode in said cathode cavity, and an auxiliary cathode contiguous to but outside of and directed toward said capacitative elements so as to introduce electrons between said elements and thereby change the capacitance and oscillation frequency.

2. A magnetron having an anode providing a cathode cavity and radiating vanes providing cavity resonators therebetween, straps extending between said vanes and constituting capacitative elements, a main cathode coaxially in said cathode cavity from which electrons will be emitted radially toward the anode, and an auxiliary cathode having an emitting area directed toward an end of the anode and toward said straps for emission of electrons the general paths whereof are toward the anode and substantially parallel to the main cathode and directed between said capacitative elements.

3. A magnetron having an anode providing a cathode cavity and radiating vanes providing cavity resonators therebetween radiating from said cathode cavity, coaxial straps extending between said vanes and constituting capacitative elements, a main cathode in said cathode cavity, and an auxiliary ring-shaped cathode opposite to and overlying end edges of said straps coaxial therewith and having an electron emitting area for directing electrons between said capacitative elements.

4. A magnetron having an anode providing a cathode cavity and radiating vanes providing cavity resonators therebetween radiating from said cathode eavity, coaxial straps extending one between alternate vanes and the other between intervening vanes and constituting each with a part of said vanes and with each other capacitative elements, a main cathode in said cathode cavity, and an auxiliary ring-shaped cathode overlying an end edge of said straps coaxial therewith and confined substantially to overlying said capacitative elements.

5. A magnetron having an anode providing a cathode cavity and radiating vanes providing a circular series of a number of cavity resonators therebetween radiating from said cathode cavity and having an end space at an end of said anode, coaxial straps extending across said radiating vanes one with clearance at its inside at the end next said end space with alternate vanes and the other with clearance at its outside with the intervening vanes and constituting with the vane with which it has clearance and between each other capacitative elements, a main cathode in said cathode cavity, and an auxiliary ring-shaped cathode in said end space coaxial with said cathode cavity and overlying said straps and vanes and said inside and outside clearances, the ends of the resonators being otherwise open to said end space.

6. A magnetron having an anode providing a cathode cavity and radiating vanes providing a circular series of a number of cavity resonators therebetween radiating from said cathode cavity and having an end space at an end of said anode, coaxial straps extending across said radiating vanes one with clearance at its inside at the end next said end space with alternate vanes and the other with clearance at its outside with the intervening vanes and constituting with the vane with which it has clearance and between each other capacitative elements, a main cathode in said cathode cavity, and an auxiliary ring-shaped cathode in said end space coaxial with said cathode cavity and overlying said straps and vanes and said inside and outside clearances, the ends of the resonators being otherwise open to said end space, and said auxiliary cathode having a plurality of equally spaced electron emissive patches and focusing means equal in number and spacing to the number of vanes and located opposite said vanes.

7. A magnetron having an anode providing a cathode cavity and a circular series of a number of evenly spaced vanes and cavity resonators radiating therefrom and having end spaces at opposite ends of said anode, coaxial straps extending one in contact with alternate vanes and the other in contact with intervening vanes and each strap successively out of contact and having clearance spaces from the vanes between the ones with which it is in contact constituting thereat and constituting between straps capacitative elements next each of said end spaces, a main cathode in said cathode cavity, and an auxiliary ringshaped cathode in each of said end spaces coaxial with said cathode cavity and directly opposite said straps and clearance spaces, the ends of the resonators being substantially otherwise open to said end spaces, and said auxiliary cathode having a plurality of equally spaced electron emissive patches and focusing collars equal in number to the said number of vanes, said patches being successively staggered and directly overlying the vanes from and including the clearance space to and including the strap remote from said clearance space in each vane.

WILLIAM E. SHOU'PP.

REFERENCES CITED The following references are of record in the file of this patent:

"Frequency Modulation and Control by Electronsa paper presented on March 4, 1947, at the I. R. E. Convention in New York, N. Y., and later found in Proceedings of the I. R. E., vol. 35, July 1947, pages 644-657. 

